Getting an earlier start is the main advantage of overwintering your pond plants. Many garden/pond stores don't start selling them in the spring until a little later than is often desired. Another advantage is having a larger plant to begin with in the spring than is usually available from suppliers. It is doubtful they will grow much in your stock tank given the amount of light available. Most likely, they will slowly shrink in size and wither away. I was successful keeping them going but it took a lot of effort. To keep them healthy and growing, I used a dedicated container (no fish), next to a western picture window and blasted the tank with high intensity plant lighting. I also had topsoil for a substrate and added fertilizer. The tank was heated. The hyacinth (and water lettuce) did fine. The real trick was reintroducing them back into the pond the next spring. While water temperature is important, interestingly, the biggest challenge was getting them acclimated to the bright, natural sunlight. They will become sunburned and die after all of your hard work so figure out some way to completely shade them and then gently increase the intensity, daily, for about a week to ten days depending upon the weather. I always waited until we had a few days of rain to bring them outside which helped.
